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If you go back and have a look at the old version of the wiki page linked by @The Annoying Pyro, there is an explanation there:

The Smelt Class Weapons blueprint was originally one Primary, Secondary, and Melee weapon of each class, but was then altered to allow any 3 (now 2) weapons from the same class, to accommodate the Engineer, Demoman, Spy, and at the time this change was made, the Sniper. This has made the blueprints marked with a dagger superfluous.